the right frequency strikes the receiver.
Solder the preprogrammed PIC 12F508 (available from
the Nuts & Volts webstore, along with the board). Note pin
1 is the square pad. Solder the R1 (10K) resistor and Q1.
Solder the four IR emitters, placing the long lead into the
Locate the IR transmitter template; cut and glue it onto
the box lid. Drill the proper holes for the LEDs. Drill
a hole for the cord. Cut off the plug of the battery
eliminator and pass it through the side hole in the box.
Determine the positive wire using a voltmeter and solder
it to its pad on the board. Solder the other wire to the
negative pad. Mount the board to the lid using two 3/8”
spacers and two 6-32 1/2” screws. Note: The LEDs will not
show a visible light when plugged in.
The TDK CHS-MSS is a five volt sensor that outputs
0-1 volts for 0% to 100% humidity. Its output can be placed
on the “amp” inputs. Pull its five volt supply from the pad
above the battery terminal. For maximum sensitivity, use a
five amplification with the op-amp; R1 = 100K; R2 = 24K.
There is a drawing at the article link for measuring the
humidity of the Earth.
Set the rotary to nine for voltages to trip if the humidity
is above a set point. Set the rotary switch to A for voltages
to trip if the humidity is below the set point.
Calculate the voltage of the sensor and multiply it by
the amplification. Set the R5 voltage to this calculated
voltage using the test point. Use three strands of #30 wire
wrap to use the humidity sensor remotely. Five volts+ can
be obtained from the extra pad next to the battery input.
Make sure the ground lead goes to the - pad of the amp
input and he sensor out lead goes to the + pad.
Parallax makes a number of gas detectors and a board
for their processing. I have put extra pads for a power
supply for driving another board. Gas detectors pull a fair
amount of power as they use a heating element. Make sure
you use a battery eliminator because they will drain a
battery in a matter of hours. Use the amplifier pads for
input, and adjust R1 and R2 for amplification.
Set the rotary to eight for voltages to trip above the
reference voltage (TP1, R5). Set the rotary to nine for
voltages to trip below the reference voltage (TP1, R5).
Jameco carries a number of reasonable pressure
sensors. These require a five volt power supply and can be
interfaced to the “amp” inputs. Most pressure and force
sensors use a strain gauge in a Wheatstone bridge
configuration, and their voltage changes with pressure. Use
the amplifier pads for input, and adjust R1 and R2 for
amplification. Set the rotary to eight for voltages to trip
above the reference voltage (TP1, R5). Set the rotary to nine
for voltages to trip below the reference voltage (TP1, R5)
This versatile circuit provides tons of applications. I’m
sure you’ll be able to implement it in many of your own
October 2013 35
MADE IN THE USA
BYPANAVISE PRODUCTS,INC .
Future items you might want to add for monitoring and
alarming include: gasses (O2, CO2, gasoline, methane,
propane, alcohol, etc.), or a radiation monitor. These will
need an additional board to function. I have added extra
pads for those who wish to program and add to this project.
I only used the comparator portion of the chip; however, the
chip has A/D converters. The possibilities are limitless. Keep
in mind that the range of the radio transmission is up to 1/2
mile. Monitoring of many sensors is now possible without
wires! (Please contact the author for details on these add-ons.)